Childs dentist app (long need advice)

My son can't have the sedation juice they give kids because to have that he has to fast an he can't fast or else he gets very combative. He fights with you, argues, doesn't co-operate, he used to get physical with me (kicking & hitting) then when school started we figured out he was a must-eat kid and I had been treating it myself by giving him food whenever he was hungry. So his last time he was needing a filling done was June 2014 so he had a bad experience and we needed to send him to a surgical centre where they did deep sedation. Now I posted before about him cracking his tooth by a kid running their bike into him and he hit concrete, so it's going to cost me 650$ to have the work done before my insurance will reimburse me, don't have that laying around exactly, so I'm looking around for other dentists that will do the work and take my insurance before hand. But since my son can't have the juice sedation and can only have laughing gas or deep sedation, if I took him to see my GP before the app is there anything she would prescribe him to keep him calmer during the app so he would be safe? Last time he kept trying to grab the drill from the dentist and got himself so worked up he ended up throwing up even though there was nothing in his system. I want him to have a good experience it's the dentist, I take him to my regular dentist for cleaning apps so he doesn't be afraid of my dentist and only major things do I take him outside our office, so if there's no other choice but to do deep sedation I'm okay with that but I don't want to put my son through the first try if it goes badly just because the dentist would rather not deep sedate him incase he does good and can co-operate. I'm just afraid that something bad will happen.
My son is also turning 6 end of August but he will regress sometimes to being 4 when he doesn't eat properly. And a 50lb child who fights with you and is 6 but with the mentality of a 4yo, I'm 27w and 5'2" an he's probably just over 4' now.